Sintered hardmetals, which are understood as sintered materials consisting of metallic sintered materials based on high-melting carbides of the metals from Groups 4b to 6b of the Periodic Table and low-melting binder metals from the iron group, in particular cobalt, have been known for a long time. They are mainly used for the machining technology and for controlling wear. For producing these sintered hardmetals from the usually pulverulent sintering materials, the metal binders are necessary which must wet the sintering material during the sintering process with alloy formation (solution). It is only in this way that the tough/hard microstructure of the sintered hardmetals, of which the WC-Co and TiC-WC-Co systems are best known, suitable for use is formed. It is also known that binders from the iron group are also suitable for other high-melting metallic sintered materials such as borides and nitrides (compare "Ullmanns Enzyklopadie der techn. Chemie [Ullmann's Encyclopedia of Industrial Chemistry]", Vol. 12, 4th Edition, 1976, Chapter "Sintered Metals," pgs. 515-521).
The systems TiB.sub.2 --Fe, Co or Ni and ZrB.sub.2 and Fe, Co or Ni have already been investigated in the 60's. It was then found that such alloys based on TiB.sub.2 with up to 20% Fe as binder are considerably harder than those based on WC-Co and TiC-WC-Co. Alloys based on ZrB.sub.2 with Co and Ni are brittle and not resistant to oxidation, whereas Fe reacts with ZrB.sub.2 to form tetragonal Fe.sub.2 B and can thus not be used as a binder (compare papers by V.F. Funke, et al and M.E. Tyrrell, et al, abstracted in the book "Boron and Refractory Borides", edited by V.J. Matkovich, Springer-Verlag, Berlin-Heidelberg-New York, 1977, in Chapter XIV, pg. 484, in conjunction with Table 7 and pg. 488, in conjunction with Table 8).
It was concluded from these results that evidently the suitable binder, which might compensate the disadvantages of the excessive brittleness and thus allow industrial use of such alloys in the field of cutting materials and other applications with high demands on the corrosion resistance, heat resistance and/or oxidation resistance, for these borides, had not yet been found (compare loc. cit., pg. 489).
Alloys based on nitrides and carbonitrides of titanium and zirconium with a very high proportion of the binder, in particular iron, (at least 50% and higher) are particularly tough, but no longer very hard (HV 1050-1175) (compare U.S. Pat. No. 4,145,213 to Oskarsson, et al). Presumably, such materials are indeed less brittle than the abovementioned boride-based systems. Because of their low hardness, however, they are unsuitable for machining hard and high temperature-resistant materials such as Sic-reinforced aluminium alloys.
Combinations based on diborides, in particular of titanium and zirconium, with carbides and/or nitrides, in particular titanium nitride and titanium carbide, and with boride-based binders such as in particular Co boride, Ni boride or Fe boride, do not lead to a solution of the problem, since although such materials are very hard and strong because of the boride binder, which is to be understood in particular as CoB, they are particularly brittle instead (compare U.S. Pat. No. 4,379,852 to Watanabe, et al).
Finally, attempts have also already been made to add graphite, which is intended to react with oxygen present during the sintering step, to the known system based on titanium boride and, if appropriate, titanium carbide with binders of iron, cobalt and nickel or alloys thereof before the mixture is sintered. In this way, it is said that cutting materials can be obtained which are both sufficiently hard and tough, so that they can be used in particular for the machining of aluminium and aluminium alloys (compare EP-B-148,821 of Moskowitz, et al, which is based on PCT Application No. WO 84/04,713). By the reaction of graphite with titanium boride in the presence of iron, however, the formation of the undesired Fe.sub.2 B phase is promoted, which is not only less hard than titanium diboride but also reduces the proportion of the ductile iron binder phase, so that the materials resulting from this are not only less hard, but also less tough.
It is therefore the object to provide mixed sintered hardmetal materials based on high-melting borides and nitrides of metals from Group 4b of the Periodic Table and low-melting binder metals consisting of iron or iron alloys, which are highly dense, very hard, tough and strong so that they can be used in particular as cutting materials for hard and high temperature-resistant materials.